The major goal of this project is to characterize virus antigens and other components expressed on the surface of infected cells which are the targets of the immune response. Monoclonal antibodies against the major surface component of measles virus, the hemagglutinin (HA), have been produced and used to characterize the biosynthesis, glycosylation, and assembly of this protein. The HA protein is being studied in strains of measles virus which differ in biological activity. Similar studies are being conducted with the fusion (F) protein. New methods for the isolation of measles virus polypeptides have been developed and are now being used to prepare pure antigens for assessment of the immune response.